1. Field of the Invention
The present invention relates to an apparatus for the metering of liquid agricultural chemicals and the like, and more specifically relates to a valve metering system which is adapted for use in such an apparatus.
2. Description of the Related Art
Various devices are known in the art intended for metering the application of liquid agricultural chemicals to the soil at a constant rate of liquid application per unit of soil area.
Pumps for the metering of liquid agricultural chemicals are disclosed, for example, in J. Blue, U.S. Pat. No. 2,696,785 and Horton et al., U.S. Pat. No. 2,811,108. In these devices anhydrous ammonia and other similar liquids useful in agriculture to the soil are applied to the soil in amounts varying with the speed of the vehicle to which the apparatus is attached.
Devices for the purpose of metering and distributing anhydrous ammonia and other similar liquids useful in agriculture from a vehicle to the soil at a constant rate of application per unit area are also known in the art. Particular examples are disclosed in Horton U.S. Pat. Nos. 2,909,191 and 3,346,006. These metering devices automatically compensate for back pressure fluctuations in the conduits leading to the distributing means.
A method and means of presetting the output rate of a centrifugal pump agricultural metering system is also disclosed in my U.S. Pat. No. 4,267,971. That system included a pump which received liquid from a supply tank and delivered it to a liquid discharge orifice means, the rate of flow through which is substantially proportional to the square root of the pressure thereon. The system also includes a line having adjustable orifice means therein controllable by the vehicle driver while the vehicle is moving for returning a portion of the pump delivery liquid to the tank and controlling upstream pressure. Orifice pressure Pn required to achieve a preselected application rate at a selected vehicle speed can be determined readily. For each such Pn there is a corresponding calculable, or ascertainable by test, pump system pressure Pc when flow to the discharge orifice means is shut off. A Pc pressure gauge is readable by the driver and also preferably a Pn gauge. Pn is first determined and then the corresponding Pc. The vehicle is moved at the selected speed with the pump being driven and flow to the discharge orifice means shut off while the driver adjusts the adjustable orifice means to preset the Pc corresponding to the determined Pn. Flow to the discharge orifice means can then be started to obtain substantially the preselected application rate at substantially all the vehicle speeds.